Accelerating groundwater extraction contributing to rise in sea levels

Posted 27 September 2011

The global rate of groundwater extraction has accelerated massively since 1950 (image credit: NASA).

A study calculating a new estimate of the quantity of groundwater extracted globally over the last century has quantified the contribution of that water to rising sea levels.

While groundwater is extracted for a variety of purposes, the majority eventually finds its way to the sea.

The study measured how much of this extracted groundwater water has ended up in the oceans by looking at changes in the levels in 46 well-studied aquifers.

This was then extrapolated to the rest of the world, producing an estimate of about 4500 cubic kilometres of water extracted from aquifers between 1900 and 2008.

That contributed 1.26 centimetres (7.4%) to the overall rise in sea levels of 17 cm during the same period.

While sea-levels are already well-known to have risen during that time because of melting ice and expansion due to warming, quantification of the contribution of extracted groundwater to sea-level rise provides new insight into causal factors.

Although the estimated contribution of extracted groundwater to sea-level rise may seem relatively small, the rate of extraction has accelerated massively since 1950, particularly in the past decade. Almost a third of the groundwater total was extracted between 2000 and 2008 (1300 cubic kilometres), causing 0.36 cm (12.9%) of the 2.79-cm rise in that time.

"I was surprised that the depletion has accelerated so much," says study author Leonard Konikow of the United States Geological Survey..

It's not clear if the acceleration will continue. Konikow points out that some developed countries are cutting back on aquifer use and even trying to refill them when there is plenty of rainfall. "I would like to see that implemented more," he says.

"While there remain significant uncertainties, Konikow's estimate is probably the best there is for groundwater depletion," says John Church of CSIRO Marine and Atmospheric Research in Hobart, Tasmania.

Konikow, Church and colleagues have used the data to compare the contributions of the different sources of sea-level rise and found that aquifer depletion is almost as significant as the ice melt in Greenland and Antarctica combined.

Source: New Scientist.

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